Carburetor secondary throttle nudging mechanism



June 27, l1967 J. T. BlcKHAus, ETAL 3,328,007

CRBURETOR SECONDARYTHROTTLE NUDGING MECHANISM 4 Sheets-Sheet 1 Filed Sept. 25, 1965 Y INVV'ENTOR JAMES T. BlcKHAus BLBERT w. `ZUBv ATTORNEY June 27, 1967 .1.1'. BlcKHAus ETAL 3,328,007

l CARBURETOR SECONDARY THROTTI-JE NUDGING MECHANISM Filed Sept. 23, 1965 4 Sheets-Sheet 2 June 27, 1967 J. T. BlcKHAUs ETAL 3,328,007

CARBURETOR SECONDARY THROTTLE NUDGING MECHANISM Filed Sept. 23, 1965 4 Sheets-Sheet 3 PRI. THROTTLE lOPEN `Pif-2|. THROTTLE'OPEN lF107. FIG. l2.

June 27, 1967 J. T. BICKHAUs ETAL 3,328,007

CARBURETOR SECONDARY THROTTLE NUDGING MECHANISM Filed sept. 23, 1965 4 sheets-sheet 4 United States Patent 3,328,007 CARBURETOR SECGNDARY THROTTLE NUDGING MECHANISM .lames 'I'. Bickhaus and Albert W. Zub, St. Louis, Mo.,

assignors to ACF Industries, Incorporated, New York,

N. Y., a corporation of New Jersey Filed Sept. 23, 1965, Ser. No. 489,656 4 Claims. (Cl. 261-23) This invention relates to carburetors of the two-stage variety having an air valve anterior the fuel supply nozzles of the secondary mixture conduit. In one of its aspects the invention relates to mechanism for partially opening the secondary throttles of a four barrel carburetor prior to the time that the secondary mixture conduit is called upon to deliver fuel to the associated internal combustion engine. In another of its aspectsthe invention relates to mechanism for preparing the `fuel nozzles of the secondary mixture conduits for delivering fuel.

A well-known Vtype of multistage carburetor is a four barrel carburetor having a pair of primary conduits or barrels and a pair of secondary conduits or barrels. Such a carburetor is provided with `a conventional choke valve anterior the mixture zone of the primary conduits and is provided with an air valve anterior the fuel nozzles of the secondary conduits. In such a carburetor the choke valve for the primary barrels is responsive to engine temperature and restricts the air flow into the primary barrels only during warm-up of the engine. The air valve ofthe secondary conduits opens in response to air flow through the secondary side of the carburetor and in effect meters the air thereto. While this description will relate principally to such a four barrel carburetor, it is intended that the discussion also apply to a two barrel carburetor having a single primary barrel and a single secondary barrel. p

In a carburetor such as that just described, the primary barrels are capable of operating the car through a wide range of normal operating conditions up to land including normal highway speeds. However, for acceleration and for heavy load conditions such as climbing a steep incline, the secondary barrels are provided to supply the additional air and fuel lrequired for theseiconditions. It is the usual mode of operation that the primary throttles are opened up to about 60 degrees from the closed position without effecting the secondary throttles in any way. It is also common during the operation of the multistage carburetor that when the secondar-y barrels are called into play, the primary throttles are opened to the full Iopen position and the secondary throttles are also open to the full opened position rather rapidly. When this is done the primary fuel system continues to supply fuel throughout the entire opening range of the primary throttle, but the secondary fuel system which has been inactive up until this time experiences a slight delay in supplying fuel. Because air is already moving through the secondary side of the carburetor, this momentary lack of fuel may -result in a slight hesitation or stumble in the operation of the motor vehicle.

The provision of an air valve anterior the secondary fuel nozzle has been of some help in overcoming this hestitation or stumble. However, under some circumstances it has been found that an improvement over this condition can be realized through the practice of the invention. According to the invention, throttle linking mechanisms are supplied which operate the primary and secondary throttles in a sequence such that by a partial opening of the lsecondary throttles the secondary fuel nozzles can be prepared for delivery of fuel without actually delivering fuel until the time that the secondary barrels are called upon to provide a substantial portion of the fuel-air mixture required for heavy load conditions.

32,328,007 Patented June 27, 1967 The above is accomplished by a linkage which allows the primary throttle to open in the range of- 30 to 50" from the closed position without effecting the position of the secondary throttles. Thereafter the linkage will open' the secondary throttles slightly (in the range of 3 to 1'()5 degrees) and the throttles will then maintain approximately this same relation throughout an additional range of opening of the primary throttle. Further opening of the primary throttle from approximately to 65 to its full open position will result in the opening of the secondary throttle to its full open position. The effect of this sequence of operation of the respective throttles is that the primary side of the carburetor provides air and fuel for a proper air-fuel mixture Iand the secondary side of the carburetor supplies only a small amount of ai-r until `such time as the secondary is called on for power. This small amount of air can be compensated for by the fuel calibration of the primary side so that normal operation is sustained.

During the interval of time that the secondary throttles are slightly open, there will be created within the bore of the secondaries a slight depression which will have the eiect of drawing fuel part way up to the secondary fuel nozzle, but the depression is insufficient to cause fuel to flow through the nozzles. Thus upon further lopening of the secondary throttle, fuel is available instantly to the secondary side and there will be no hesitation or stumble in the operation of the vehicle.

It is an object of the invention to provide mechanism whereby the fuel nozzle of the secondary conduits of a multistage carburetor can be prepared to discharge fuel prior to the time that fuel is required to be delivered.

It is another object of the invention to provide throttle linkages for connecting the primary and secondary throttles of a multistage carburetor for sequentially opening the primary and secondary throttles in such a manner that through a part of the range of the primary throttle movement the secondary throttle will be opened only a slight amount and thereafter will be opened to its full extent.

Further objects, advantages and features of the invention will be seen through a perusal of the following specification, the claims, and in the drawing, in which:

FIGURE l is a top plan View of a four barrel carburetor constructed -according to the invention;

FIGURE 2 is an end view of the carburetor of FIG- URE 1;

FIGURE 3 is a sectional view through the bores of a primary and secondary of the carburetor;

FIGURES 4 through 6 illustrate one form of throttle linkages at different position in the operation of the carburetor;

FIGURE 7 is a plot of primary throttle opening versus secondary throttle opening;

FIGURES 8 through l1 illustrate another form of throttle linkages shown in various positions of the respect-ivethrottles, and

FIGURE 12 is a plot of primary versus secondary throttle positions for the embodiment of FIGURES 8 through ll.

The principles of two-stage carburetion are well-known in the art and a typical two-stage carburetor employing an air valveis exemplified in the patent to Otto Henning, 2,832,576, -dated Apr. 29, 1958. Reference is hereby made to the Henning patent for an explanation of suitable idle fuel systems and main fuel systems as well as for the operation of the air valve of the secondary' barrels and for typical throttle linkages for sequentially opening the primary and secondary throttles.

Referring now to the drawing and in particular .to FIG- URE 1, there is shown generally at 10 a two-stage four barrel carburetor having a pair of primary barrels 12 and a pair of secondary barrels 14. The primary and secondary barrels are indicated by dash lines for the reason that the primary barrels are locked from view by a choke plate 16 and the seconda'ry barrels are blocked from view by an air valve 18. The carburetor is shown mounted on the intake ange 11 of an internal combustion engine and is hel-d in place by a plurality of bolts 13. A fuel inlet 15 is provided for communication by way of a conduit 17 with a pump 19, which in turn communicates by way of a further conduit with a fuel tank F. The carburetor is provided with an air horn 20 having a partition 22 which divides or separates the primary barrels from the secondary barrels.

If desired, the carburetor may be provided with a thermostatic choke control unit 24 which may be Operatively connected `by way .of suitable links and levers to the choke shaft 26 which is journaled within a portion of the air horn for rotational movement.

The air valve 18 is mounted upon a shaft 27, also journaled into the air horn portion `of the carburetor. The air valve is biased toward a normally closed position by a coil spring 28. To accommodate the coil spring 28 there is provided an opening or slot 29 in the air valve 18. Air valve 18 fits the air horn closely at the outer edge thereof but some clearance is provided at the inner edge as shown at 31. The clearance 31, together with the opening 29, will admit some air without movement of the air valve.

Referring to FIGURES 2 and 3, it will be noted that air valve 18 is mounted on shaft 27 in an off-center manner. Thus when air is flowing through the secondary barrels of the carburetor, the force of the air causes the air valve to rotate counterclockwise as shown in FIGURE 3 against the bias of spring 28. Since the air valve is responsive air movement, it serves also as a metering element to meter the quantity of air flowing past the air valve and the air valve assumes a position in accordance with the amount of air flowing by it.

The primary side of the carburetor is provided with a throttle shaft 41, having a throttle plate 42 mounted thereon. The secondary portion of the carburetor is provided with a throttle shaft 43, having a throttle plate 44 mounted thereon for rotational movement in the bore of the carburetor. Throttle plate 44 is much larger than throttle plate 42 and may under some circumstances require a greater initial force to begin opening movement because of this greater size. It is an advantage of the invention that extra turning effort for the secondary throttle is provided by the linkages hereinafter to be described.

The primary side of the carburetor is provided with an idle fuel system shown in part and designated generally at 50 and a main fuel nozzle cluster 51 having a main fuel nozzle 52. These fuel systems communicate with a fuel bowl having a oat and needle valve as is well-known in the art. The secondary bore is provided with a main fuel system indicated generally at 54 and a main fuel nozzle 55. The secondary main fuel system also communicates with a fuel bowl having a float and needle valve. In fact the secondary fuel system can be supplied with fuel from the same fuel bowl as the primary fuel systems.

In a two-stage carburetor having a secondary of the type herein disclosed, fuel is caused to ow through the main fuel nozzle by a combination of factors. Referring to FIGURE 3, when the secondary throttle plate 44 is in its closed position there is no ow of air through the carburetor and, of course, no fuel is flowing in the secondary side. Upon opening the throttle 44 to a wide open position, the central portion of the bore is exposed to a reduced pressure because of the reduced pressure in the manifold under the carburetor. This reduced pressure will serve in part to draw fuel out of the nozzle 55 and will also serve to allow air pressure from above to force the air valve 18 downwardly in proportion to the amount of air required by the engine when the throttle valve 44 is open. After air begins movement through the secondary bore, there also comes into play the movement of the air itself which aids in drawing fuel out of the nozzle 55.

Thus it will be seen that under some circumstances there can be a condition by which the ow of air through the carburetor secondary is initiated so rapidly that fuel cannot be drawn upwardly through the fuel passage in the carburetor and then out into the nozzle 55 in such a manner as to provide a correct air-fuel ratio. Such a deciency is of short duration because the fuel does begin to flow and once the flow is started the movement of air over the nozzle increases the flow to satisfy the demands of the engine.

It has been found that if the secondary throttle 44 can be opened slightly in advance of the need for the greater volume of air that can be supplied by the secondary side of the carburetor, fuel can be drawn part way up into the fuel system of the secondary barrel to prepare the nozzle for immediate flow of fuel when called upon. This slight opening of the secondary throttle will cause a small amount of air to ow through the secondary bore, and this amount of air can pass through the clearance 31 and the slot 29 of the air valve 1S without necessarily disturbing it from its closed position.

Reference is now made to FIGURES 2, 4, 5 and 6 where one form of throttle control mechanism is shown. A lever 60 is fixed to the end of primary shaft 41 for rotational movement therewith. Lever 60 has an arm 61 and -a second arm 62. Arm 62 serves as a positive closer for the secondary throttle. Rotatably mounted on shaft 41 is a loose lever 64. Lever 64 is caused to rotate by a tab 65 on lever 60 which moves into engagement with a surface 66 of lever 64 to cause movement.

Mounted on secondary shaft 43 is a lever 70 having an extension with an elongated slot 72 and a somewhat shorter slot 73 located near the center of rotation of lever 70. There is also provided an extension 74 for cooperation with the positive closer 62. A further extension '75 serves as a throttle opening limiter. The throttle opening limiting action is controlled by the extension 75 meeting a boss 76 on the body of the carburetor. A link 77 joins arm 61 of the primary throttle lever and slot 72 of the secondary throttle lever. Another link '78 connects arm 64 with the slot 73 of the secondary throttle lever.

In considering the operation of the throttle nudging mechanism just described, it is necessary to understand the mode of operation of the two fuel systems of the primary bores. In most conventional carburetors the primary bores are equipped with a primary fuel circuit and a main fuel circuit. These are arranged in such a fashion that the primary circuit supplies all the fuel during idling and through low part-throttle operation. When the pri mary throttle has been opened some given amount, there is a transition from the idle fuel circuit to the main fuel circuit. During this transition the ow of idle fuel substantially ceases and the flow of fuel from the main nozzles increases to the required amount. At the end of the transition period, for all practical purposes, only fuel from the main fuel nozzle is owing. Since this is true, it is desirable that the secondary throttle nudging mechanism come into play during the period of transition or at the end `of the transition while the primary throttle is still in a part-throttle position. The transition from idle fuel to main fuel circuits can take place at as low as 20 of opening of the primary throttle, but may be as late as 40 or more. Thus, the initiation of secondary throttle nudging will be regulated to substantially correspond to the transition period of the primary bore.

With the foregoing in mind and further with reference to FIGURES 2 through 6, as the primary throttle is rotated the lever 60 rotates in a counterclockwise direction, as seen in FIGURE 2, and by way of extension 61 moves link 77. When the throttle is closed, link 77 has the end next the secondary lever arm in a section of slot 72 such that no movement of the secondary throttle occurs. With further rotation of the primary throttle to the transition point, link 77 moves to the end of slot 72 (see FIGURE 4). During this interval of movement the arm 64 does not move, hence link 78 does not move. Also at this time link 78 ts into the slot 73 near the lefthand portion as viewed in FIGURE 2. With further rotation of the primary throttles, as shown in FIGURE 5, link 77 pulls lever 70 clockwise a small amount. This small movement results in an opening of the secondary throttle 'by an equivalent amount, as indicated by the arc of FIGURE 5. At the same time link 78 is pulled through the length of slot 73 and comes to rest against the end of the slot shown at the right in FIGURE 5.

Upon completion of the movements just discussed, the primary throttle has been opened approximately 60 from its closed position and the secondary throttle is now ready to come into operation to deliver the much larger quantity of air the secondary bores are capable of delivering. Continued movement of the primary throttle from the position shown in FIGURE 5 results in tab 65 contacting the surface 66 to 'cause movement of the loose lever 64, which by way of link 78 picks up lever 70 of the secondary throttle mechanism to rapidly open the secondary throttle from the slightly open position just described to as much as its fully open position in accordance with demands placed on the carburetor by the operator of the vehicle The full open position of the primary and secondary throttles is illustrated in FIGURE 6*. It is seen in that figure that by way of lever extension 64 link 78 has picked up the secondary throttle and moved it to the full open position. At the same time, link 77 has moved backwardly in slot 72. This has come about because the arm 70 moves much more rapidly when link 78 is pulling on it than it does when link 77 is actuating the arm. As shown in FIGURE 6, lever arm. 78 is prevented from going beyond the full open position by virtue of the fact that extension 75 comes to rest against a boss 76 on the carburetor body.

A noteworthy advantage of the throttle nudging mechanism just described is that there is a mechanical advantage available to initiate opening of the secondary throttle. The secondary throttles in a carburetor such as that illustrated in the drawings are quite large with respect to the size of the primary throttles. Because an secondary throttle will begin to open and will slowly open continuously until the point of primary throttle opening is reached a-t which it is desired to open the secondaries to their full extent. This point is shown by a sharp upward inflection in the graph `of FIGURE 7.

Referring now to FIGURES 8 through 1l, there is shown another embodiment of the invention. Mounted on primary throttle shaft is a( fixed lever 80 and a loose lever 82. Lever 80 is provided with an extension or tab 81 for engaging a surface 83 -of lever arm 82. When such engagement is made, the tab 81 causes the arm 82 to rotate. The secondary throttle shaft 43 is provided with a lever arm 84 having a slot 85 and a tab 86. The tab 86,"upon rotation of the lever arm 84, will come to rest engine may be operating with substantial manifold vacy uum at the time the secondary throttles are called into play, substantial opening force may under some circumstances be required. To this end in the embodiment just described the lever'arm length of extension 61 is relatively short, while the lever arm length out to the slot 72 of the Secondary throttle is relatively long. Thus considerable initial opening force is available for opening the secondary throttles without making an undesirable force that would be felt at the foot pedal by an operator. Once the vacuum has lbeen broken by partial opening of the secondary throttle, then the longer lever extension 64 by way of link 78 picks up the much shorter effective lever arm length of slot 73 of the secondary throttle, and rapid opening at relatively small effort is accomplished.

Illustrated in FIGURE 7 is a plot of secondary throttle position versus primary throttle position. This graph is presented without numerical iigures for throttle opening for the reason that considerable variation is possible. As mentioned earlier, the slight opening of the secondary throttle can be accomplished from somewhere in the vicinity of 20 of primary throttle opening to 40 or even more of primary throttle opening. In similar fashion, the amount that the secondary throttle can be opened without drawing fuel through the secondary main fuel nozzle is limited in accordance with the amount of air that can be passed over and around the air valve without creating a depression under the air valve suffi- .cient to actually start fuel flowing. This usually will be in a range of 2 to 10 of secondary throttle opening with .a 5 preferred amount. Accordingly, FIGURE 7 illustrates that at some point of primary throttle opening the against a boss 88, which limits the opening of the secondary throttle. A link 89 connects lever arm 82 to lever arm 84 by way of the slot 85.

. A guide 94 is fastened to the base 88 by a bolt 90. Guide 94 is provided with a ledge 91 and a guiding surface 92.

Operation of the throttle nudger of FIGURES 8 through 11 is initiated through rotation of the primary throttle shaft 41, which in turn causes lever arm 82 to rotate (counterclockwise). After a predetermined amount of rotation, tab 81 contacts surface i83 to cause arm 82 to rotate, also counterclockwise. At this time link 89 will start to move. The end of link 89 that passes through slot initially rests upon ledge 91. As arm 82 continues to rotate, link 89 causes arm 84 to move in a clockwise direction, which movement is continued until the end of link 89 clears the ledge 91. Thereafter continued movement of arm 82 results in the end of link 89 dropping downwardly in the slot 85 Without further movement of the arm 84. The guiding surface 92 prevents the arm 84 from rotating back toward the closed position during the interval of time that the link is dropping downwardly through the slot. When the end of link 89 reaches the bottom yof slot 85, continued movement of arm 82 results in rapid movement of arm 84 t-o bring the secondary throttle to its full open position. The closing sequence is the reverse of that just described.

As in the embodiment of FIGURES 2 through 6, the linkage shown in FIGURES 8 through l1 provides a mechanical advantage to initiate the opening of the secondary throttle by virtue lof 4the longer effective lever arm during the first par-t of the opening movement.

FIGURE l2 is -a plot of secondary throttle position versus primary throttle position for the embodiment of FIGURES 8 through 1'1. It will be noted that after an initial nudging of the secondary throttle, the secondary throttle remains at the same degree of angular opening until the primary throttle has moved through a substantial range, 4after which time both throttles will open together to the full open position.

Various modifications will occur to one skilled in the art, which are within the scope of the appended claims.

We claim:

1. A multistage carburetor for an internal combustion engine comprising:

(A) a primary mixture conduit and a secondary mixture conduit,

(B) at least one fuel circuit for each -of said conduits,

said fuel circuit being .adapted to supply fuel for miX- ing with air in said conduits,

(C) a foot pedal actuated throttle valve for said primary conduit, said valve being m-ounted for rotation in said conduit on a primary throttle shaft,

(D) a fixed lever and a loose lever mounted on an end of said primary throttle shaft,

(E) a secondary throttle valve rotatably mounted on a secondary throttle shaft in said secondary conduit,

(F) an arm fixed to an end of said secondary shaft, said arm having lirst and second secondary throttle positioning surfaces,

(G) linking means linking at least one of said primary levers to said arm, said linking means including means to engage the said first secondary throttle positioning surface of said arm during an intermediate portion =of rotation of said primary shaft to partially open (B) at least one fuel circuit for each of said conduits,

said fuel circuit being adapted to supply fuel for mixing With air in said conduits,

(C) a f-oot pedal actuated throttle valve for said primary c-onduit, said valve being mounted for rotation in `said conduit on a primary throttle shaft,

(D) a fixed lever and a loose lever mounted on an end of said primary throttle shaft,

(E) a secondary throttle valve rotatably mounted on a secondary throttle shaft in said secondary conduit,

(F) an arm fixed to an end of said secondary shaft,

(G) a curved elongated slot in said arm and a short slot in said arm,

(H) a link connecting said fixed lever to said elongated slot, and

(I) a connecting rod connecting said loose lever to said short slot.

3. A multistage carburetor for an internal combustion engine comprising:

(A) a primary mixture conduit and a secondary mixture conduit,

(B) at least lone fuel circuit for each of said conduits,

said fuel circuit being adapted to supply fuel for mixing with air in said conduits,

(C) a foot pedal actuated throttle valve for said primary conduit, said valve being mounted f-or rotation in said conduit on a primary throttle shaft,

(D) a fixed lever and a loose lever mounted on an end and adapted to impart rotary movement t-o said arm ing said ledge and said guiding surface so that they Will coact with an end of said linking means in such a manner that upon initial movement of said loose lever and said linking means, the said end of said said secondary throttle and to engage the said second- 5 linking means Will be supported by said ledge at ary throttle positioning surface of said arm during a constant radial distance from the axis of said secfurther rotation of said primary shaft to further open -ondary shaft until a predetermined movement of said said secondary throttle, and arm has been completed and said guiding surface will (H) means for causing said linking means for sequencoact with said end through further movement of said tially engage said first `and second secondary throttle 10 loose lever to retain said arm in predetermined open positioning surfaces. relationship and upon further movement of said loose 2. A multistage carburetor for an internal combustion lever the said end will coact with said slot to impart engine comprising: further rotation to said arm.

(A) a primary mixture conduit and a secondary mixture 4. A multistage carburetor for an internal combustion conduit, 15 engine comprising:

(A) a primary mixture conduit and a secondary mixture conduit, each of said conduits being provided with a fuel circuit adapted to supply fuel for mixing with air in said c-onduits,

(1B) a foot pedal actuated throttle valve for said primary c-onduit, said valve being mounted on a pri-- mary throttle shaft for rotational movement in said conduit,

(C) a fixed lever and a loose lever mounted lon an endv of said primary throttle shaft, said loose lever being provided with a contacting surface and said fixed lever being provided with a tab, said tab being adapted to engage said surface to impart rotational movement t-o said loose lever,

(D) a secondary throttle valve mounted on a secondary throttle shaf-t for rotational movement .in said secondary conduit,

(E) an arm fixed to an end `of said secondary shaft and having an elongated slot and a short slot therein,

(F) a link connecting -said fixed lever to said elongated slot, and

(G) a rod connecting said loose lever to said short slot, said elongated slot being at a greater radial distance from its cen-ter Eof rotation than said short slot.

References Cited UNITED STATES PATENTS ,of Said primary throttle Shaft, Klt'tlel et al. (E) a secondary throttle valve rotatably mounted on a 207491100 6/ 19 5 6 Carlsonsecondary throttle shaft in said secondary conduit, 2,807,448 9/1957 MOTOL (F) an arm fixed to an end of said secondary shaft, 2,832,576 4/'1958 Henning- (G) an augularly disposed slot in said arm, 2,836,404 5/1958 Carlson et al. (H) linking means linking said loose lever to said slot `2,914,052 11/ 1959 Read.

HARRY B. THORNTON, Primary Examiner.

RONALD R. WEAVER, Examiner.

upon rotation of said loose lever, and (-1) fixed guide means on said arm, said guide means having a ledge and a guiding surface, means position- 

1. A MULTISTAGE CARBURETOR FOR AN INTERNAL COMBUSTION ENGINE COMPRISING: (A) A PRIMARY MIXTURE CONDUIT AND A SECONDARY MIXTURE CONDUIT, (B) AT LEAST ONE FUEL CIRCUIT FOR EACH OF SAID CONDUITS, SAID FUEL CIRCUIT BEING ADAPTED TO SUPPLY FUEL FOR MIXING WITH AIR IN SAID CONDUITS, (C) A FOOT PEDAL ACTUATED THROTTLE VALVE FOR SAID PRIMARY CONDUIT, SAID VALVE BEING MOUNTED FOR ROTATION IN SAID CONDUIT ON A PRIMARY THROTTLE SHAFT, (D) A FIXED LEVER AND A LOOSE LEVER MOUNTED ON AN END OF SAID PRIMARY THROTTLE SHAFT, (E) A SECONDARY THROTTLE VALVE ROTATABLY MOUNTED ON A SECONDARY THROTTLE SHAFT IN SAID SECONDARY CONDUIT, (F) AN ARM FIXED TO AN END OF SAID SECONDARY SHAFT, SAID ARM HAVING FIRST AND SECOND SECONDARY THROTTLE POSITIONING SURFACES, 